Device packaging has been a major obstacle to the successful implementation of wafer-scale integration (WSI). WSI implies that a large integrated circuit is created which covers the entire substrate of a silicon wafer, possibly as large as six inches in diameter. Instead of dicing the wafer into smaller chips for individual packaging, the wafer-scale circuit remains whole, intensifying the normal packaging problems of integrated circuits.
Integrated circuits, in general, are very susceptible to damage caused by excessive strain in the silicon wafer. Such strain can damage the fine line circuitry, alter the electrical properties of the various materials present, or even fracture the wafer itself. The wafers are generally rigidly attached to a support structure in some means to protect the wafer from externally applied loads, such as shock loading, bending, etc. However, this protective structure itself may produce forces on the wafer which can cause damage to the wafer. Excessive strain can be the result of differential thermal expansion of the wafer and its support structure, and the mechanism for attaching the wafer to the support structure may also stress the wafer due to high clamping forces, tensile, compressive, or bending loads, etc., that it applies to the wafer.
Previous embodiments of the WSI packaging are shown in FIG. 1. The wafer 1 is rigidly attached to the substrate 2 by a system of clamps 3 and/or adhesive bond 4. In either case, the substrate 2 material must be carefully chosen to closely match the coefficient of thermal expansion of the wafer 1, in order to minimize the strain on the wafer 1 that would be caused by differential expansion of the two materials. Some materials that have been used are molybdenum and various ceramics. These materials are expensive and difficult to manufacture, and are not necessarily the best thermal conductors available.